The first step is to establish the link between Jira and Confluence:

1. Navigate to Administration > Applications > Application links in Jira.
2. Enter your Confluence URL into the Application textbox and click the Create new link button. Jira should automatically detect the target application as Confluence. If, for some reason, it does not, make sure you select Confluence as the Application type when prompted, as shown in the following screenshot:

We also need to enable the Remote access API (disabled by default) in Confluence:

1. Log in to Confluence as a Confluence administrator.
2. Navigate to Administration > Further Configuration.
3. Click on Edit, scroll down, and check the Remote API (XML-RPC & SOAP) option.
4. Click on Save to apply the change:

The remote access API is now enabled.